Unitarian Universalism (otherwise referred to as UUism or UU) is a liberal religion characterized by a "free and responsible search for truth and meaning". Unitarian Universalists assert no creed, but instead are unified by their shared search for spiritual growth.

These traditions are summarized by the Six Sources and Seven (or, in some congregations, eight) Principles of Unitarian Universalism, documents recognized by all congregations who choose to be a part of the Unitarian Universalist Association. These documents are "living", meaning always open for revisiting and reworking. Unitarian Universalist congregations include many atheists, agnostics, deists, and theists and have churches, fellowships, congregations, and societies around the world. The roots of Unitarian Universalism can be traced back to Protestantism and liberal Christianity, more specifically to Unitarianism and Christian universalism. Unitarian Universalists state that from these traditions comes a deep regard for intellectual freedom and inclusive love. Congregations and members seek inspiration and derive insight from all major world religions.

The beliefs of individual Unitarian Universalists range widely; they can include, but are not limited to, Religious humanism, Judaism, Christianity, Islam, Hinduism, Sikhism, Buddhism, Taoism, Syncretism, Neopaganism, Atheism, Agnosticism, New Age, Omnism, Pantheism, Panentheism, Pandeism, Deism, and teachings of the Baháʼí Faith.

The Unitarian Universalist Association (UUA) was formed in 1961 through the consolidation of the American Unitarian Association, established in 1825, and the Universalist Church of America, established in 1793. The UUA is headquartered in Boston, Massachusetts and serves churches mostly in the United States. A group of thirty Philippine congregations is represented as a sole member within the UUA. The Canadian Unitarian Council (CUC) became an independent body in 2002. The UUA and CUC are two of the seventeen members of the International Council of Unitarians and Universalists.